I did performance benchmark for roaring bitmaps when I added bloomfilters (hyperloglog also shares the same bitset impl) to Orc and Hive. I found that roaring bitmap is good at compression at the cost of speed. In a JMH benchmark, observed around ~10x slowdown during insert and probe when using roaring bitmap vs the raw bitset (long array without compression). So it essentially boils down to speed vs space tradeoff.
Thanks Prasanth On Dec 11, 2017, at 3:58 PM, Nitin Vijayvargiya <nitinvija...@gmail.com<mailto:nitinvija...@gmail.com>> wrote: Hi David, Thanks for the response. Yea, bloom filters are mostly for existential checks. I'm looking for a way to preprocess data, and then perform operations like union/intersection between them to find counts. Example: Number of distinct users visiting website A over the last 5 days (union), intersected with the number of distinct visitors visiting website B over the last 10 days (union). Hyperloglog is the right tool for this, but if someone has done performance benchmarking between HLL and Roaring BitMap, it would save me a lot of time. Thanks, Nitin On Fri, Dec 8, 2017 7:08 PM, David Capwell dcapw...@gmail.com<mailto:dcapw...@gmail.com> wrote: Think bloom filter that's more dynamic. It works well when cardinality is low, but grows quickly to out cost bloom filter as cardinality grows. This data structure supports existence queries, but your email sounds like you want count. If so not really the best fit. On Dec 8, 2017 5:00 PM, "Nitin Vijayvargiya" <nitinvija...@gmail.com<mailto:nitinvija...@gmail.com>> wrote: Hi all, I'm working on speeding up distinct count calculations, and it looks like roaring bitmaps (RB) is the newest and meanest way for set operations. Anyone here have experience with them? How was the performance compared to hyperloglog and EWAH? A quick google search showed me that it's easier to find UDF implementations of hyperloglog in presto and hive, but if the hype is real, it might be worth spending the time to incorporate RB. Also, if anyone can point me to reliable implementations of UDFs using RB, I would love to check it out and test it myself =) Happy Holidays! Nitin
